[Zack77]

2006 325i; today I changed my plugs (114k miles and stock to my knowledge), and during this process I had also disconnect what I believe to be the eccentric shaft sensor and reconnected it (noticed oil around it). Immediately after starting the car I had a rough idle, I then took it back into the garage and removed and reinstalled all plugs and coils-it ran fine for about twenty minutes until I let it idle again and then it proceeded to have an extremely rough idle (and a distinct sound like pennies rattling really loud.
I then reset the check engine light and proceeded without any issues. I checked for a misfire by pressing the throttle down a bit and got a misfire on 5&6. Then I put the old plugs back in and it was much worse (1&5&6). The old plugs were definitely mixed up in order.
So what is my best option; to buy all new coils as well or could it be because of the gap from the old stock plugs?

[Three_thirty_I]

A few questions:

Since this rough idle was after replacing the plugs, have you tried reinstalling the old plugs to see if this changes anything?

How much oil did you find in the Eccentric Shaft Sensor plug? And did you clean this oil out?

Which brand and model of plugs did you fit? And did you check their gaps?

[ssmith96]

At that mileage I wouldn't be shocked if you're coils were on their way out... I know its funny timing but it could be the case. I had a misfire after doing my plugs that turned out to be from a coil so I just replaced all 6 as a preventative measure. Also make sure the electrical connectors for the coils are all the way, they do need a good hard push.

[Zack77]

There was no oil in the actual connector for the eccentric shaft sensor, just around it. The plugs are Bosch and are gapped properly. Yes I did try reinstalling the old plugs

[Three_thirty_I]

How do you know which cylinders are misfiring? If you can pinpoint them, then you could move the coil packs from the unaffected cylinders to the affected ones to see if the problem follows.

[Zack77]

It was quite a bit, I mixed the coils around and then the misfire moved-replaced those two coils and it's running fine again now, thanks for the replies everyone.

[Three_thirty_I]

So then it seems it was a few coils that were at fault! Glad you have it sorted out!